Security thread and process for the preparation thereof

ABSTRACT

A partially metallized film having a dyed region and a transparent region alternately at an each regular interval on a major surface thereof is useful as a security thread to be embedded in a security paper. The partially metallized film for a security thread is conveniently prepared by printing a fluorescent pigment or dyestuff at a regular interval on a transparent film, applying a water-soluble ink over the dyed regions and to another selected portions of the film at a regular interval, depositing a layer of a metal on the entire surface of the transparent film including the water-soluble ink layer; and washing the metal deposited film with water to remove the portion of the metal layer deposited on the water-soluble ink layer.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation-in-partCIP) application of U.S. Ser. No. 09/623,862 filed on Sep. 1, 2000, which is now abandoned and claims priority thereon pursuant to 35 USC section 120.

FIELD OF THE INVENTION

[0002] The present invention relates to a security thread having unique security features suitable for use in security articles and process for the preparation thereof. Specifically, the present invention relates to a partially metallized film for a security thread having a dyed region and a transparent region alternately at an each regular interval on a major surf ace thereof, in the form of a figure, character or pattern.

BACKGROUND OF THE INVENTION

[0003] Security documents such as bank notes, stocks, bonds, checks, warrants and identification cards need to be guarded by antifalsification measures and they are of ten made from a security paper having a security element in the form of fibers, strips or threads embedded therein.

[0004] For example, GB 2,213,098 discloses a partially metallized film strip, used as a security thread, which has metal-free portions in the form of a pattern, design, indicia, etc. to provide a continuous metal path along the length of the strip.

[0005] Further, Japanese Laid-open Patent Publication No. 216795/1988 teaches a security strip having a metallized pattern on the surface of a transparent film.

[0006] U.S. Pat. No. 5,876,068, on the other hand, discloses a security element comprising a transparent plastic film having an opaque coating extending over the element with recesses corresponding to patterns to be introduced and in areas congruent with the recesses, at least one of coloring substances and luminescent substances which cause the patterns to differ from the security element and from the opaque coating by color contrast under suitable light conditions.

[0007] There still exists a need to develop various security threads having enhanced unique features.

SUMMARY OF THE INVENTION

[0008] It is, therefore, an object of the present invention to provide a security thread having enhanced security features, suitable for use in a security paper.

[0009] It is another object of the present invention to provide a process for the inventive security thread.

[0010] It is still another object of the present invention to provide a security paper containing the inventive security thread.

[0011] In accordance with an aspect of the present invention, there is provided a partially metallized film for a security thread having a dyed region and a transparent region alternately at an each regular interval on a major surface thereof, the regions being in the form of a figure, character or pattern.

[0012] In accordance with an aspect of the present invention, there is provided a process for the preparation of the inventive partially metallized film for a security thread, which comprises:

[0013] (i) printing a fluorescent pigment or dyestuff at a regular interval on a major surface of a transparent film in the form of a figure, character or pattern;

[0014] (ii) applying a water-soluble ink over the pigment or dyestuff-printed regions and to another selected portions of the major surface of the film at a regular interval in the form of a figure, character or pattern;

[0015] (iii) depositing a layer of a metal on the entire surface of the transparent film including the water-soluble ink layer; and

[0016] (iv) washing the metal deposited film with water to remove the portion of the metal layer deposited on the water-soluble ink layer.

BRIEF DESCRIPTION OF DRAWING

[0017] The above and other objects and features of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawing, wherein:

[0018] FIGS. 1 to 4 show the steps of forming a partially-metallized film having a transparent region in the form of a set of characters and a dyed region in the form of another set of characters in accordance with one embodiment of the present invention; and

[0019]FIGS. 5 and 6 illustrate other embodiments of security threads in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The inventive security thread in the form of a partially metallized film is characterized by having a dyed region and a demetallized (i.e., transparent) region alternately at an each regular interval on a major surface thereof. In the present invention, the dyed region and the demetallized region may be in the form of a figure, character or pattern and be preferably present in a longitudinal direction of the film.

[0021] The substrate which may be used in the inventive security thread, may be made from any material known in the art such as a polyester (e.g., polyethylene terephthalate (PET)), polyvinyl chloride, polypropylene and the like.

[0022] The inventive partially metallized security thread may be prepared as follows:

[0023] At first, the fluorescent pigment or dyestuff is applied to a major surface of a transparent base film, as a substrate, at a regular interval. The fluorescent pigment or dyestuff may be any one conventionally used in the art and it may be applied in the form of a character, pattern or figure, or a combination thereof, preferably by a gravure printing method.

[0024] Thereafter, a water-based ink, which is soluble in water, is applied over the pigment or dyestuff-printed regions to form a mask for the dyed portion and simultaneously, the water-based ink is applied and to another selected portions of the major surface of the film at a regular interval, in the form of a character, pattern or figure. The water-based ink may be any one conventionally used in the art.

[0025] Subsequently, a layer of a metal is deposited on the entire surface of the film including the printed ink layer. The deposition may be carried out by vacuum metallizing methods, which are well known by a skilled person in the art. Representative examples of the metal suitable for forming the metal layer are aluminum, tin, a metal alloy (e.g., Co and Ni), silver and the like. The thickness of the metal layer ranges from 1 Å (Aungstrom) to 2 μm.

[0026] The metal-deposited film is then washed with water, preferably with brushing or spraying, to remove the portion of the metal layer deposited on the water-soluble ink layer, to obtain a partially metallized film having a dyed region and a demetallized region alternately at an each regular interval on a major surface thereof.

[0027] The security thread of the present invention has a thickness and width suitable for use in security documents, e.g., a thickness ranging from about 15 to 35 μm and a width ranging from 0.5 to 5 mm.

[0028] The security thread of the present invention may be preferably embedded between two sheets of paper formed separately on a paper making machine and subsequently brought together to form a security paper having an embedded security thread.

Embodiments of the Invention

[0029] FIGS. 1 to 4 show the steps of forming a partially-metallized film having a transparent region in the form of a set of characters and a dyed region in the form of another set of characters, alternately, in accordance with one embodiment of the present invention.

[0030] Referring to FIG. 1, a fluorescent dye stuff or pigment composition such as LUMILUX CD 305, CD 316 or PAPILION is applied in the form of a set of characters (2) on the surface of a transparent polyester substrate (10) at a regular interval by a gravure printing method.

[0031] Subsequently, as shown in FIG. 2, a water-based ink is printed on the film to form a mask (30) of the printed characters portion (2) and, simultaneously, a design (31) in the form of another set of characters.

[0032] Aluminum is deposited on the resulting film by a vacuum deposition method to form an aluminum layer (4) at a thickness of 1 Å (Aungstrom) to 2 μm over the entire surface of the film, as shown in FIG. 3.

[0033] Finally, the portions of the aluminum layer deposited on the mask (30) and the design (31) are removed by washing with water, while brushing, to obtain an aluminum-deposited film (1) comprising transparent characters (5) (corresponds to the design (31)) and printed characters (2) positioned in a transparent region (10).

[0034]FIGS. 5 and 6 illustrate other embodiments of security threads prepared by the inventive process.

[0035] Specifically, FIG. 5 shows a security thread (1) having alternating metal-deposited portion (4) comprising transparent characters (5), and transparent substrate region (10) comprising colored characters (2) at a regular interval. Further, FIG. 6 shows a security thread (1) obtained by a chain of imprinting alternating colored (2) and metallized links (4) on a base film (10).

[0036] While the invention has been described with respect to the specific embodiments, it should be recognized that various modifications and changes may be made by those skilled in the art to the invention which also fall within the scope of the invention as defined by the appended claims. 

1. A partially metallized film for a security thread having a dyed region and a transparent region alternately at an each regular interval on a major surface thereof, the regions being in the form of a figure, character or pattern.
 2. The partially metallized film for a security thread according to claim 1, wherein the film is prepared by a process comprising the steps of (i) printing a fluorescent pigment or dyestuff at a regular interval on a major surface of a transparent film in the form of a figure, character or pattern; (ii) applying a water-soluble ink over the pigment or dyestuff-printed regions and to another selected portions of the major surface of the film at a regular interval in the form of a figure, character or pattern; (iii) depositing a layer of a metal on the entire surface of the transparent film including the water-soluble ink layer; and (iv) washing the metal deposited film with water to remove the portion of the metal layer deposited on the water-soluble ink layer.
 3. The partially metallized film for a security thread according to claim 2, wherein the metal is selected from the group consisting of aluminum, tin, silver and an alloy of cobalt and nickel.
 4. The partially metallized film for a security thread according to claim 1, wherein the film has a thickness ranging from 15 to 35 μm and a width ranging from 0.5 to 5 mm. 